Metal sound board for pianos and the like



April 21, 1925.

F. FRANKEL METAL soimb" BOARD FOR PIANOS AND THE LIKE Fne d au 24, 1923jhvenfor:

Patented Apr. 21, 1925.

UNITED s'r FRIDOLF FRANKEL, 0F STOGKHOLM, SWEDEN.

METAL SOUND BOARD FOR PIANO-S AND THE LIKE.

Application filed August 24, 1923. Serial No. 659,113.

To aZZ 10720222 in may concern.

Be it known that I, FnrnoLr FRANKEL, a subject of the King of Sweden,residing at Stockholm, in the Kingdom of Sweden, have invented new anduseful Improvement in Metal Sound Boards for Pia-nos and the like. ofwhich the following is a specification.

As is now well known, the resounding power of sounding boards andsounding plates becomes better the higher the inherent tension is in theboard orplate. The purpose of the present invention is to increase theresounding power of such sounding boards or plates which are provided ina manner previously described with corrugations or bent-up folds or ribshaving approximately V-shaped cross section formed in the plate orboard, and the invention is characterized by that the portions of theplate or board between said projecting corrugations or ribs arecontracted or shortened in relation to said corrugations or ribs byfolds, ridges or the like formed in said portions by pressing or thelike. Owing to the said portions of the plate or board being contractedor shortened in this manner in relation to the intermediate corrugationsor ribs, there will of course be set up a certain tension between thesaid portions of the plate and the corrugations which in creases theresounding power. There is also produced a certain bending of thecorrugations or ribs so that the plate or board obtains a certaincup-shape or convexity which also increases its capability of supportingthe pressure from the strings when the plate is used as a sounding boardin a piano.

As an example of the invention a sounding board for a. piano constructedaccording to the present invention is illustrated in the accompanyingdrawing. Fig. 1 shows the front side of the sounding-board, Fig. 2 is asection on the line II-H in Fig. 1, and Fig. 3 is a section on the lineTIT-TIT in Fig. 1, Figs. 2 and 3 both showing the curvature or convexityof the board in an ex.- aggerated way. Figs. 4 and 5 show to a largerscale detail views of the sections of the board illustrated in Figs. 2and 3 respectively.

The sounding board illustrated in the drawing is formed, in a mannerpreviously described, of a whole continuous metal plate 1 in which thereare formed corrugations or bent-up folds or ribs 2 which have anapproximately U-shaped or V-shaped cross section. The said ribs 2preferably project above the front side of the sounding-board 1 to whichside the bridge or bridges 5 over which the strings are stretched, aresecured. 1V hen attaching the plate 1 to the fastening rim 3 'bysoldering, welding or in any other suitable manner, each rib 2 issqueezed or pressed together in suitable manner at its ends 4 at theedges of the plate, so that the cross section of said ends 4: of theribs beintermediate portions of the ribs, and in this manner the edgesof'the sounding board become contracted or shortened so that the portionof the plate within said edges obtains a certain cup-shape or convexity,and simultaneously a certain tension will be produced in the same.

According to the present invention there are formed in the portions 6 ofthe board between the projecting corrugations or ribs 2 folds or ridges7. Such folds or ridges 7 may be formed in the plate, for instance, bypressing the plate between dies one of which has a ridge or tooth ofapproximately V- shaped cross section and the other of which has agroove of corresponding shape. These folds or ridges? are formed in theplate 1 after the corrugations or ribs 2 have been produced in the platewhich may be effected in any manner well known in the art for producingcorrugated plates. Owing to said folds or ridges 7 in the plate betweenthe ribs 2 the said portions 6 of the plate will of course becomeshortened in relation to the ribs 2, so that an increased tension isproduced between the said portions 6 of the plate and the ribs 2, andtherefore the .7

resounding power of the board is also in creased. The said shortening ofthe plate between the ribs will of course also be'conducive to furtherincrease the cup-shape or convexity of the plate. The said folds orridges 7 may be formed in the plate before or after the plate is securedto the rim 3, and they are naturally located at an angle to the ribs 2though not necessarily at right angles to the same, and further theridges 7 between the different ribs 2 need not be in alignment.

Owing to the high tension produced according to the present invention ina sounding plate its resounding power is lncreased comes slightlynarrower than that of the to such great extent that, for instance, whenthe plate is used as a sounding board of a piano there is obtained inthe instrument a great, noble and beautiful. tone heretofore neverattained, Sound boards according to the invention may of course also beused for other stringed musical instruments, and they may also be builtinto the walls of concert halls, lecture-rooms and the like in order toimprove the acoustic properties cl such localities.

I claim: l. A metal sounding plate provided with entuip ribs havingapproximately V- shaped cross section and. projecting above the -frontside of the sounding: plate, the portions of the plate between said ribsbeing contracted in relation to said ribs in a direction substantiallyparallel to said ribs.

2. A metal sounding plate provided with bent-up ribs havingapproximately vshaped cross section and projecting above the front sideof the sounding plate, and having folds in. the portions of the platebetween said ribs contracting said port-ions n relation to said ribs.

3. A metal, sounding plate provided with bent-up ribs having;approximately =1 shaped cross section and projecting above the frontside of the sounding plate, each of said ribs being pressed together atits ends at the edges of the sounding' plate, for the purpose ofproducing contractions ot the edge portions of the sounding plate, theportions of the plate between said ribs being contracted in relation tosaid ribs.

4 A metal sounding plate provided with bent-up ribs havingapproxiniately V- shaped cross section and projecting abore the frontside of the sounding" plate, eaen of said ribs being pressed together atits endsv at the edges of the sounding plate, tor the purpose ofproducing contract-ioiis oi the edge portions of the sounding plate, and

havin folds in the )ortions ot the )late h l 1 between said ribscontracting said portions in relation to said lllOS.

FRIDULF FRANKEL.

